The present invention generally relates to optical semiconductor microelectronics, and more particularly to epitaxial crystal multilayer structures and a manufacturing method thereof. The invention also relates to semiconductor light-emitting devices with enhanced light emission output intensity.
In recent years, red light-emitting diodes (LEDs) have become more widely used in the manufacture of electronic equipment. Several types of LEDs have been developed to date. A double-heterostructure LED is one example. A rear-surface reflection LED is another example. These LEDs come with enhanced luminance, and hence offer extended usability and applicability, such as for use with a indoor lamps and display devices, as well as outdoor display devices.
However, in spite of the foregoing advances in this technology, it is also true that there are continuous demands for a further increase in luminance and a further decrease in manufacturing cost. To satisfy such demands, great efforts have been made to study several subjects involving the film thickness of the epitaxial layer, the carrier density or concentration, the crystal growth temperature settings and other factors. Unfortunately, no efforts have been reported as being successful in demonstrating significant advantages leading to accomplishment of further improvements in luminance, least at present.
For these reasons, it still remains difficult to meet luminance specifications as demanded, which in turn makes it difficult to provide an improvement in the manufacturing yield, while reducing the costs therefor.
In view of the foregoing, it may be appreciated by those skilled in the semiconductor art that there remains an unmet need for an epitaxial wafer capable of offering highly enhanced luminance with increased stability and reliability, along with an improved manufacturing method, as well as a light-emitting diode using the same.
It is therefore an object of the present invention to provide an improved optical semiconductor structure which avoids the problems encountered with the prior art.
It is another object of the invention to provide an epitaxial wafer structure which is capable of increased perfomance and reliability.
It is yet another object of the invention to provide an improved method of forming an epitaxial multilayer lamination wafer which is capable of increased light emission output and reliability while reducing the complexity of manufacture and the costs therefor.
It is still another object of the invention to provide an improved light-emitting device which is capable of increased light emission output and reliability while reducing the complexity of manufacture and the costs therefor.
It is a further object of the invention to provide a high-performance/high-reliability light-emitting multilayer epitaxial semiconductor device structure which is capable of maximizing the output light luminance characteristics and light emission stability, while reducing the complexity and costs.
To attain the foregoing objects, in accordance with one aspect of the present invention, a double-heterostructure epitaxial crystal plate or wafer is provided which has on its p-type compound semiconductor substrate a multilayer lamination including a p-type compound semiconductor clad layer, a p-type compound semiconductor active layer and a n-type compound semiconductor clad layer which are sequentially formed by liquid-phase epitaxial growth techniques. Each interface between the p-type compound semiconductor clad layer and p-type compound semiconductor active layer and between the p-type compound semiconductor active layer and n-type compound semiconductor clad layer measures 1xc3x971017 atoms per cubic centimeter (cmxe2x88x923) or less in oxygen concentration.
With such specific numerical control of the oxygen concentration near or around the active layer, it becomes possible to adjust the light emission output intensity, which in turn ensures that the light output intensity decreases with an increase in oxygen concentration, whereas it increases with a decrease in oxygen concentration. Accordingly, letting the oxygen concentration be set at 1xc3x971017 cmxe2x88x923 may enable the light emission luminance to increase by 30%, or more or less, as compared with the prior art. Preferably, the compound semiconductor materials for use in forming the multilayer wafer structure may be gallium arsenide (GaAs), gallium phosphide (GaP), gallium indium phosphide (GaInP), or equivalents thereto. Note here that the principles of the invention may also be applicable to epitaxial wafers with a rear-surface reflection structure, which eliminates use of the p-type compound semiconductor, substrate from the multilayer structure mentioned supra.
In accordance with a further aspect of the invention, the foregoing double-heterostructure epitaxial wafer may be fabricated or manufactured by a specific method as follows. While employing a non-doped compound semiconductor polycrystalline having an oxygen density or concentration less than or equal to 1xc3x971016 cmxe2x88x923, sequentially grow by liquid-phase epitaxial techniques a p-type compound semiconductor clad layer, a p-type compound semiconductor active layer and an-type compound semiconductor clad layer on a p-type compound semiconductor substrate in this order. During fabrication, each interface between the p-type compound semiconductor clad layer and p-type compound semiconductor active layer and the interface between the p-type compound semiconductor active layer and n-type compound semiconductor clad layer are specifically set to be less than or equal to 1xc3x971017 cmxe2x88x923 in oxygen concentration. With such a fabrication technique, it is possible to manufacture a high-performance epitaxial wafer having a maximized light emission luminance with increased production yield and reduced costs.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.